1. Technical Field
The invention relates to projection technology and, particularly, relates to a projection system for use in liquid crystal based projectors.
2. Description of Related Art
Referring to FIG. 5, a liquid crystal based projector 99, such as liquid crystal display (LCD) projector or liquid crystal on silicon (LCoS) projector, typically includes a light source unit 98, and a liquid crystal panel 97 (e.g., LCD panel or LCoS panel). The light source unit 98 includes a light source 981 and a condensing lens 982 for collecting and directing light from the light source 981 onto the LCD panel for modulation to produce a projection image.
Also referring to FIG. 6, the result of an experiment that was conducted to determine how a contrast value of the projection image varies with an incidence angle α of the beam of polarized light directed onto the liquid crystal panel 97 is shown. It can be inferred that contrast degradation of the projection image is mainly caused by polarized light with large incidence angle. Therefore, high contrast of the projection image can be achieved by reducing the incidence angle α. In the art, an aperture is employed to reduce the size of the beam of polarized light 95 to reduce the incidence angle α. However, this aperture will also reduce brightness of the projection image.
Therefore, it is desirable to provide a projection system for use in the liquid crystal based projector, which can overcome the abovementioned problems.